Rubber mixture and pneumatic vehicle tire

ABSTRACT

A rubber mixture and a pneumatic vehicle tire including a rubber mixture containing the following constituents: 15 to 55 phr of at least one natural polyisoprene and/or 15 to 55 phr of at least one synthetic polyisoprene and 15 to 85 phr of at least one polybutadiene and 60 to 100 phr of at least one carbon black and 1 to 10 phr of at least one anti-ozone wax, wherein the anti-ozone wax contains unbranched hydrocarbons having the following chain length distribution including at least the three ranges A and B and C: range A: hydrocarbons having 26 to 31 carbon atoms, range B: hydrocarbons having 32 to 36 carbon atoms, range C: hydrocarbons having 37 to 47 carbon atoms, wherein the relative mass fractions of the ranges A to B to C are 0.7-1.5 to 0.6-1.4. The tire contains the rubber mixture at least in an outer component.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of international patentapplication PCT/EP2014/060377, filed May 21, 2014, designating theUnited States and claiming priority from European application13174984.8, filed Jul. 3, 2013, and the entire content of bothapplications is incorporated herein by reference.

FIELD OF THE INVENTION

The disclosure relates to a rubber mixture and to a pneumatic vehicletire.

BACKGROUND OF THE INVENTION

It is known that pneumatic vehicle tires include constituents whichsignificantly retard the aging and oxidation of the rubbers and otherconstituents present and which therefore positively influence thedurability over a relatively long lifetime of the tire.

Furthermore, however, it is also known that aging inhibitors andantiozonant waxes present in the external components of pneumaticvehicle tires can migrate to the surface, where they form a visiblefilm. This phenomenon, known as blooming, has adverse consequences inturn for the visual appearance of the pneumatic vehicle tire.

U.S. Pat. No. 6,201,049 discloses a rubber mixture for the sidewall ofpneumatic vehicle tires, comprising a wax which contains a componenthaving 45 or more carbon atoms in an amount of 3 to 10 wt %.

U.S. Pat. No. 7,498,366 as well describes a rubber mixture whichcomprises paraffin wax for the sidewall of pneumatic vehicle tires.

U.S. Pat. No. 5,296,129 discloses a rubber mixture which comprisesnatural rubber and polypropylene and also a paraffin wax mixture, ineach of which the amount of hydrocarbons having 31 to 44 carbon atoms isnot less than 2 percent by weight.

A common characteristic of the publications cited is that thecomposition of the rubber mixture is intended to improve the visualappearance and/or the cracking resistance.

SUMMARY OF THE INVENTION

Against the background of the prior art, then, the object on which thedisclosure is based is that of providing a rubber mixture for externalcomponents of pneumatic vehicle tires that exhibits a furtherimprovement in terms of blooming, with no adverse effect, and/or evenwith improvement, in the aging resistance and the other physicalproperties, such as tensile strength and/or hardness and/or tearproperties and/or rebound elasticities.

The object is achieved by the rubber mixture comprising the followingconstituents:

-   -   15 to 55 phr of at least one natural polyisoprene and/or 15 to        55 phr of at least one synthetic polyisoprene,    -   15 to 85 phr of at least one polybutadiene,    -   60 to 100 phr of at least one carbon black, and    -   1 to 10 phr of at least one antiozonant wax, the antiozonant wax        comprising unbranched hydrocarbons with the chain length        distribution below, consisting of at least the three ranges A        and B and C:        -   i. range A: hydrocarbons having 26 to 31 carbon atoms        -   ii. range B: hydrocarbons having 32 to 36 carbon atoms        -   iii. range C: hydrocarbons having 37 to 47 carbon atoms,    -   the relative proportions of the ranges of A to B to C being 0.7        to 1.5:1:0.6 to 1.4.

Surprisingly, the rubber mixture with the combination of the statedconstituents exhibits particularly low blooming, and this is manifestedin an improved visual appearance of the rubber mixture after acorresponding duration.

The phr unit used in this specification (parts per hundred parts ofrubber by weight) is the conventional quantitative unit for mixtureformulations in the rubber industry. The metered quantity of the partsby weight of the individual substances here is always based on 100 partsby weight of the overall composition of all of the rubbers present inthe mixture.

The rubber mixture of the invention contains 15 to 55 phr of at leastone natural polyisoprene and/or 15 to 55 phr of at least one syntheticpolyisoprene.

The amount of natural and/or synthetic polyisoprene is preferably 18 to55 phr, more preferably 18 to 45 phr.

This means that a combination of natural and synthetic polyisoprene isalso conceivable.

In one particularly preferred embodiment, the rubber mixture contains 35to 45 phr of at least one natural and/or synthetic polyisoprene. Thismeans that a combination of natural and synthetic polyisoprene is alsoconceivable. In this embodiment, however, the component in question ispreferably natural polyisoprene. A rubber mixture of such a kindexhibits good processing properties and also, especially in the flangeprofile of pneumatic vehicle tires, particularly good bloomingcharacteristics and also comparatively good tear and abrasionproperties, especially after aging.

The natural polyisoprene and the synthetic polyisoprene in question mayinclude all of the types known to the skilled person.

The rubber mixture of the invention contains 15 to 85 phr, preferably 51to 85 phr, of at least one polybutadiene.

In one particularly preferred embodiment of the invention, the rubbermixture contains 51 to 75 phr, very preferably 55 to 65 phr, of at leastone polybutadiene. A rubber mixture of this kind exhibits goodprocessing properties and also, especially in the flange profile ofpneumatic vehicle tires, particularly good blooming characteristics andalso comparatively good tear and abrasion properties, especially afteraging.

The polybutadiene (BR, butadiene rubber) may include all of the typesknown to the skilled person. These include, among others, the so-calledhigh-cis and low-cis types, where butadiene rubber with a cis fractiongreater than or equal to 90 wt % is referred to as of high-cis type, andbutadiene rubber with a cis fraction of less than 90 wt % is referred toas of low-cis type. An example of a low-cis polybutadiene is Li-BR(lithium-catalyzed butadiene rubber), with a cis fraction of 20 to 50 wt%. An example of a high-cis polybutadiene is Nd-BR (neodymium-catalyzedbutadiene rubber). With Nd-BR, particularly good vulcanizate propertiesare achieved in the rubber mixture. The polybutadiene used may have beenendgroup-modified.

According to an advantageous development, there is at least one furtherdiene rubber present in the rubber mixture, and in this context alldiene rubbers known to the skilled person are contemplated. Inaccordance with the advantageous development, there is preferably atleast one styrene-butadiene rubber present in the rubber mixture. Thestyrene-butadiene rubber (styrene-butadiene copolymer) may besolution-polymerized styrene-butadiene copolymer (S-SBR) having astyrene content, based on the polymer, of about 5 to 45 wt % and a vinylcontent (amount of 1,2-bonded butadiene, based on the overall polymer)of 5 to 70 wt %, which may be prepared, for example, using lithiumalkyls in organic solvent. The S-SBR may also have been coupled and/orendgroup-modified and/or modified along the carbon chain(backbone-modified).

Also possible for use, however, are emulsion-polymerizedstyrene-butadiene copolymer (E-SBR) and also mixtures of E-SBR andS-SBR. The styrene content of E-SBR is about 15 to 50 wt %, and thetypes that may be used are those known from the prior art and obtainedby copolymerization of styrene and 1,3-butadiene in aqueous emulsion.

The rubber mixture of the invention contains 60 to 100 phr, preferably61 to 100 phr, of at least one carbon black. A rubber mixture of thiskind exhibits good processing properties and also, especially in theflange profile of pneumatic vehicle tires, particularly good bloomingcharacteristics and also comparatively good tear and abrasionproperties, especially after aging.

In one preferred embodiment of the invention, the rubber mixturecontains 61 to 80 phr, more preferably 67 to 80 phr, of at least onecarbon black.

All types of carbon black known to the skilled person are conceivablehere.

Preference is nevertheless given to using at least one carbon blackwhich has an iodine adsorption number to ASTM D 1510 of 15 to 100 g/kg,preferably 30 to 100 g/kg, more preferably 50 to 100 g/kg, and a DBPnumber to ASTM D 2414 of 30 to 150 ml/100 g, preferably 50 to 150 ml/100g, more preferably 100 to 150 ml/100 g. By this means, particularly goodrolling resistance and/or tear properties are obtained in the pneumaticvehicle tire in use.

It is also conceivable for two different carbon blacks, both fallingwithin the ranges stated above, to be used in the rubber mixture of theinvention.

According to one preferred embodiment of the invention, at least onecarbon black is used that has an iodine adsorption number to ASTM D 1510of 80 to 100 g/kg and a DBP number to ASTM D 2414 of 115 to 127 ml/100g.

The rubber mixture may, in addition to carbon black, also include otherknown polar and/or nonpolar fillers.

Carbon black is preferably included as the sole filler or as the mainfiller in the rubber mixture of the invention, meaning that the amountof carbon black is significantly greater than the amount of any otherfillers included. Where not only carbon black but also a further filleris included, the further filler is preferably silica. It is thereforealso conceivable for the rubber mixture of the invention to includecarbon black and silica, such as, for example, 60 to 100 phr of carbonblack, preferably 61 to 100 phr, more preferably 61 to 80 phr of carbonblack, very preferably 67 to 80 phr of carbon black, in combination with0.1 to 10 phr of silica.

The silicas in question may be the silicas known to the skilled personand suitable as a filler for tire rubber mixtures. It is particularlypreferred, though, if a finely divided, precipitated silica is used thathas a nitrogen surface area (BET surface area) (to DIN ISO 9277 and DIN66132) of 35 to 350 m²/g, preferably of 35 to 260 m²/g, more preferablyof 100 to 260 m²/g, and very preferably of 130 to 235 m²/g, and a CTABsurface area (to ASTM D 3765) of 30 to 400 m²/g, preferably of 30 to 250m²/g, more preferably of 100 to 250 m²/g, and very preferably of 125 to230 m²/g. Silicas of this kind lead to particularly good physicalproperties of the vulcanizates. There may also be resulting advantagesin the processing of the mixture, as a result of a reduction in themixing time for unchanged product properties, leading to improvedproductivity. Examples of silicas that may be employed are thereforethose of the Ultrasil® VN3 type (trade name) from Evonik, and alsohighly dispersible silicas, known as HD silicas (for example, Zeosil®1165 MP from Rhodia).

In order to improve the processing properties and to attach the silicaand any other polar fillers present to the diene rubber, it is possibleto use silane coupling agents known to the skilled person in rubbermixtures.

With particular preference, however, the rubber mixture is free fromfurther fillers other than carbon black; in this preferred embodiment,in other words, the rubber mixture contains 0 phr of a further filler.In this embodiment, accordingly, the metered addition of a second filleris unnecessary. Zinc oxide is not considered a filler in this context.

Preferably, the rubber mixture comprises 1 to 10 phr of at least oneantiozonant wax, the antiozonant wax comprising unbranched hydrocarbonswith the chain length distribution below, including at least the threeranges A and B and C:

-   -   range A: hydrocarbons having 26 to 31 carbon atoms    -   range B: hydrocarbons having 32 to 36 carbon atoms    -   range C: hydrocarbons having 37 to 47 carbon atoms,

the relative proportions of the ranges of A to B to C being 0.7 to1.5:1:0.6 to 1.4.

Conceivable in this context are all antiozonant waxes known to theskilled person. The antiozonant wax is preferably a paraffin wax.

The chain length of hydrocarbons is a function of the number of carbonatoms. The chain length distribution is determined by gas chromatographycoupled with a flame ionization detector (GC-FID). The procedure andevaluation are in accordance with the EWF (European Wax Federation)method.

For each chain length of the unbranched hydrocarbons, the relativeproportion is ascertained. The “relative proportion of an unbranchedhydrocarbon” in the context of the present invention means theproportion of the peak area or signal area of a hydrocarbon, relative tothe entirety of all peak areas or signal areas of the antiozonant wax.

The relative proportion of each range A, B, and C is calculated bysumming the individual relative proportions of the respectivelyassociated unbranched hydrocarbons (n-alkanes).

It is preferred for the ratio of unbranched (n, normal) to branched(iso) hydrocarbons in the antiozonant wax, based on the entirety of theantiozonant wax, in other words the entire chain length distributionincluding the ranges A, B, and C, to be 95:5 to 65:35.

The skilled person understands unbranched hydrocarbons to be n-alkanes.

It is preferred, furthermore, if the relative proportion of each of theindividual unbranched hydrocarbons having a number of carbon atoms of 26to 47 in the antiozonant wax does not exceed 5.5%. This means that thechain length distribution of the unbranched hydrocarbons having 26 to 47carbon atoms is comparatively flat.

With a chain length distribution of this kind in the antiozonant wax,blooming in the rubber mixture of the invention is particularly low andtherefore good.

The antiozonant wax contains, as described above, unbranchedhydrocarbons having a chain length of 26 to 47 carbon atoms. Theantiozonant wax may further contain unbranched hydrocarbons having achain length of 25 or fewer carbon atoms and/or 48 or more carbon atoms.

It is preferred, moreover, if the antiozonant wax comprises n-alkaneshaving 25 or fewer and 48 or more carbon atoms in an overall proportionof 0 to 18%. In this case the overall proportion of the n-alkanes having25 or fewer carbon atoms is preferably 5% to 12%, and the overallproportion of the n-alkanes having 48 or more carbon atoms is preferably0 to 6%.

The antiozonant wax described is included in amounts of 1 to 10 phr,preferably 1 to 5 phr, more preferably 1 to 3 phr in the rubber mixture.

The rubber mixture may further comprise customary adjuvants in customaryparts by weight. These adjuvants include

-   -   a) aging inhibitors, such as, for example,    -   N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD),    -   N,N′-diphenyl-p-phenylenediamine (DPPD),    -   N,N′-ditolyl-p-phenylenediamine (DTPD),    -   N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD),    -   2,2,4-trimethyl-1,2-dihydro-quinoline (TMQ),    -   b) activators, such as, for example, zinc oxide and fatty acids        (for example, stearic acid),    -   c) resins, such as phenolic resins and/or aliphatic resins,    -   d) mastication aids, such as, for example,        2,2′-dibenz-amidodiphenyl disulfide (DBD),    -   e) plasticizers, as described below.

The proportion of the total amount of further adjuvants is 3 to 150 phr,preferably 3 to 100 phr, and more preferably 5 to 80 phr.

Within the overall proportion of the further adjuvants there are also0.1 to 4 phr, preferably 0.1 to 3.8 phr, more preferably 2 to 3.8 phr,of zinc oxide (ZnO).

The ZnO in question may be any of the types of zinc oxide known to theskilled person, such as, for example, ZnO granules or powders. The zincoxide conventionally used generally has a BET surface area of less than10 m²/g. Also used, however, may be what is called nano-zinc oxide,having a BET surface area of 10 to 60 m²/g.

In the rubber mixture there may also be 0 to 70 phr, preferably 0.1 to60 phr, preferably 0.1 to 50 phr, of at least one plasticizer, which isincluded among the adjuvants. This plasticizer is selected from thegroup consisting of mineral oils and/or synthetic plasticizers and/orfatty acids and/or fatty acid derivatives and/or resins and/or facticesand/or glycerides and/or terpenes and/or biomass-to-liquid oils (BTLoils) and/or rubber-to-liquid oils (RTL oils) and/or liquid polymers,with mineral oils being particularly preferred. Where mineral oil isused, it is preferably selected from the group consisting of DAE(distilled aromatic extracts) and/or RAE (residual aromatic extract)and/or TDAE (treated distilled aromatic extracts) and/or MES (mildextracted solvents) and/or naphthenic oil.

The vulcanization is carried out in the presence of sulfur or sulfurdonors with the aid of vulcanization accelerators, it being possible forcertain vulcanization accelerators to act as sulfur donors at the sametime. Sulfur or sulfur donors and also one or more accelerators areadded to the rubber mixture in the final mixing step, in the quantitiesstated. The accelerator is selected in this case from the groupconsisting of thiazole accelerators and/or mercapto accelerators and/orsulfenamide accelerators and/or thiocarbamate accelerators and/orthiuram accelerators and/or thiophosphate accelerators and/or thioureaaccelerators and/or xanthogenate accelerators and/or guanidineaccelerators. Preferred is the use of at least one sulfenamideaccelerator selected from the group consisting ofN-cyclohexyl-2-benzothiazolesulfenamide (CBS) and/or

N,N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) and/orbenzothiazyl-2-sulfene morpholide (MBS) and/orN-tert-butyl-2-benzothiazylsulfenamide (TBBS). In one preferredembodiment of the invention, the rubber mixture comprises CBS and/orTBBS as accelerator(s). Particularly good tear properties of the rubbermixture are achieved as a result.

The rubber mixture preferably contains elemental sulfur in amounts of0.5 to 3 phr, preferably 1 to 3 phr, more preferably 1 to 2.7 phr, verypreferably 1.8 to 2.9 phr.

According to one particularly preferred embodiment, the rubber mixturecontains 2.0 to 2.4 phr of sulfur.

A rubber mixture of this kind exhibits good processing properties andalso, especially in the flange profile of pneumatic vehicle tires,particularly good blooming characteristics and also comparatively goodtear and abrasion properties, especially after aging.

The rubber mixture preferably contains at least one sulfenamideaccelerator in amounts of 0.1 to 4 phr, more preferably 0.1 to 3 phr,very preferably 0.5 to 3 phr. According to one particularly preferredembodiment, the rubber mixture contains 2.1 to 2.9 of at least onesulfenamide accelerator.

A rubber mixture of this kind exhibits good processing properties andalso, especially in the flange profile of pneumatic vehicle tires,particularly good blooming characteristics and also comparatively goodtear and abrasion properties, especially after aging.

The instant rubber mixture is produced by the method customary in therubber industry, where first of all a base mixture with all of theconstituents apart from the vulcanizing system (sulfur and substancesinfluencing vulcanization) is produced in one or more mixing stages.Adding the vulcanizing system in a final mixing stage produces thecompleted mixture. The completed mixture is further processed by anextrusion procedure, for example, and is converted into the appropriateform.

A further object of the present disclosure is that of providing apneumatic vehicle tire which is distinguished by an improved visualappearance in terms of blooming, with no adverse effect, and/or evenwith improvement, in the aging resistance and the other properties ofthe tire, such as handling behavior and/or wet braking and/or tearproperties and/or rolling resistance.

This object is achieved by the pneumatic vehicle tire including at leastone rubber mixture as described above in at least one component. All ofthe observations stated above concerning the constituents and theirfeatures are valid here.

The component in question is preferably an external component, morepreferably a sidewall and/or a flange profile. Very preferably it is aflange profile.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The disclosure is now to be elucidated in more detail using comparativeexamples and working examples which are summarized in Table 1.

The comparative mixture is labeled C, the inventive mixture I.

Mixture production took place under customary conditions in two stagesin a laboratory tangential mixer. Test specimens were produced from allof the mixtures by vulcanization, and these test specimens were used fordetermination of the physical properties typical of the rubber industry.For the above-noted tests on test specimens, the test methods employedwere as follows:

-   -   Shore A hardness (Shore A unit, abbreviated ShA) at room        temperature (RT) and 70° C. in accordance with DIN 53 505    -   Rebound elasticity (abbreviated rebound) at room temperature        (RT) and 70° C. according to DIN 53 512    -   Stress values at 50%, 100% and 300% elongation (modulus 50,        modulus 100 and modulus 300, respectively) at room temperature        (RT) according to DIN 53 504    -   Tensile strength and elongation at break at room temperature        according to DIN 53 504    -   Blooming: built and vulcanized tires were stored for 3 months,        protected from moisture and solar radiation, and then evaluated        visually. Class 1: satisfactory visual appearance, class 2:        adequate visual appearance, class 3: inadequate visual        appearance    -   Ozone resistance at room temperature according to DIN 53 509/DIN        ISO 1431-1        similar conditions: ozone concentration 200 pphm, ±30 pphm,        temperature 25° C.±3° C., 60%±5% atmospheric humidity, and a        static elongation between 10% and 60%, the evaluation taking        place in a method based on DIN 53 509/DIN ISO 1431-1,        evaluation: positive (no cracking) or negative (cracking)

TABLE 1 unit C1 I1 Constituents Natural rubber TSR phr 20 20Polyisoprene, synthetic phr 20 20 Butadiene rubber^(a)) phr 60 60 Carbonblack N339 phr 74 74 Aging inhibitor phr 4 4 Other adjuvants phr 17.517.5 Antiozonant wax A^(b)) phr 2 — Antiozonant wax B^(c)) phr — 2Sulfur and sulfenamide phr 4.7 4.7 accelerator Properties Tensilestrength at RT MPa 13 12 Rebound elasticity at RT % 38 38 Reboundelasticity at % 48 47 70° C. Shore hardness at RT Shore A 73 74 Shorehardness at 70° C. Shore A 69 69 Blooming class 3 1 Ozone resistancepositive positive ^(a))butadiene rubber, Nd-catalyzed, high-cis BR^(b))antiozonant wax A: Okerin ® 2122H from Paramelt, chain lengthdistribution A:B:C = 1.2:1:0.3 ^(c))antiozonant wax B: VARAZON ® 6500from Sasol Wax GmbH, chain length distribution A:B:C = 1.1:1:1

As is apparent from Table 1, the inventive rubber mixture I1, incomparison to its reference C1, exhibits much better bloomingcharacteristics, so putting the inventive mixture at a satisfactorylevel. At the same time there are no adverse effects on the otherproperties, especially the ozone resistance.

It is understood that the foregoing description is that of the preferredembodiments of the invention and that various changes and modificationsmay be made thereto without departing from the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:
 1. A rubber mixture comprising: 15 to 55 phr of atleast one natural polyisoprene and/or 15 to 55 phr of at least onesynthetic polyisoprene; 15 to 85 phr of at least one polybutadiene; 60to 100 phr of at least one carbon black; and, 1 to 10 phr of at leastone antiozonant wax, the antiozonant wax including unbranchedhydrocarbons having a chain length distribution within the ranges A andB and C: i. range A: hydrocarbons having 26 to 31 carbon atoms ii. rangeB: hydrocarbons having 32 to 36 carbon atoms iii. range C: hydrocarbonshaving 37 to 47 carbon atoms, wherein relative proportions of the rangesof A to B to C are 0.7 to 1.5:1:0.6 to 1.4.
 2. The rubber mixture asclaimed in claim 1, wherein a ratio of n to iso in the antiozonant wax,based on the entirety of the antiozonant wax, is 95:5 to 65:35.
 3. Therubber mixture as claimed in claim 1, wherein a relative proportion ofeach of the individual unbranched hydrocarbons having a number of carbonatoms of 26 to 47 in the antiozonant wax does not exceed 5.5%.
 4. Therubber mixture as claimed in claim 1, wherein the antiozonant waxcomprises n-alkanes having 25 or fewer and 48 or more carbon atoms in anoverall proportion of 0 to 18%.
 5. A pneumatic vehicle tire comprisingat least one rubber mixture as claimed in claim 1 in at least oneexternal component.